Drug delivery vehicles and pharmaceutical compositions are often used to locally deliver bioactive agents to particular locations within a subject. Many vehicles and compositions, however, are difficult to retain locally for extended periods of time. Some formulations can quickly clear (diffuse out of, migrate out of, and/or be removed by one or more active-transport or passive-transport mechanisms) from the site of administration. Rapid clearance of these vehicles and compositions can necessitate their frequent re-administration (re-dosing) in order to provide an effective treatment over a desired duration of days or months. Delivery vehicle and/or drug diffusion away from the site of administration can also induce unwanted side effects, such as inflammatory responses and systemic side effects.